While formaldehyde is a highly reactive compound that is toxic to cells and the environment, it is a common metabolic intermediate in the biological oxidation of many methylated compounds. This toxin has the ability to react with biological macromolecules by introducing nicks into double stranded DNA, cross-linking proteins to DNA and cross-linking single stranded DNA and RNA. Much of the formaldehyde that is found in our atmosphere results from the photo-oxidation of methane, oxidation of hydrocarbons released from plants and by numerous industrial products (cosmetics, cigarette smoke, automotive emissions, etc.); that contain this chemical as an ingredient. Due to the prevalence of formaldehyde in our society and its reactivity with various intracellular components, it is not surprising to find that all cells have mechanisms to remove this potentially lethal compound. Recent results have shown that the facultative formaldehyde oxidizer, Rhodobacter sphaeroides, is an ideal organism to study the biological oxidation of formaldehyde since we know this biotransformation requires an enzyme that has been identified in prokaryotes and eukaryotes. In addition, the ongoing sequencing project of the R. sphaeroides genome has identified a gene cluster that shows significant similarity to gene products of other facultative formaldehyde oxidizing eubacteria. I will use in-frame deletion mutagenesis to determine the role of each gene product within this cluster and transposon mutagenesis to identify additional proteins required to metabolize formaldehyde. Both techniques will assist in dissecting the mechanism used by cells to metabolize formaldehyde and shed new light onto the study of the biological formation and oxidation of formaldehyde.